How is it possible to reconcile the apparently irreconcilable:
that habitual physical activity may protect from heart disease, yet
exercise per se may be an important risk factor for sudden death? It
is a problem with which medicine has grappled since antiquity.

Historical
Background

The Greek physicians Hippocrates and Galen were among the first to
express an opinion on the risk of exercise on the heart. Hippocrates
attacked athleticism in his treatise on Nutrient, writing that
"...the condition of the athlete is not natural." Six centuries later
Galen wrote that "athletes live a life quite contrary to the precepts
of hygiene, and I regard their mode of living as a regime far more
favorable to illness than to health... While athletes are exercising
their professions, their body remains in a dangerous condition but,
when they give up their professions, they fall into a condition more
parlous still; as a fact, some die shortly afterwards; others live
for some little time but do not arrive at old age."

The first modern sport to attract a similar concern was rowing. In
1845, the seventh Oxford and Cambridge Boat Race was the first to be
rowed on the current course on the Thames between Putney and
Mortlake. No sooner had it moved to its longer course through the
British capital than an irate letter written by one Frederick C.
Skey, past president and fellow of the Royal College of Surgeons,
appeared in the Times, charging that "the University Boat Race
as at present established is a national folly." Skey claimed that
rowing was bringing young men to an early grave.

A scientific study published shortly thereafter by John Morgan, a
Birmingham physician, proved that Skey was in error. Morgan showed
that the life expectancy of university oarsmen was not reduced. If
anything, it was slightly longer than that of the average Englishman
of the period.

Almost a century later the issue was revived by a letter that
appeared in the Journal of the American Medical Association
stating that all members of the 1948 Harvard rowing crew had since
died "of various cardiac disease". The assertion was enthusiastically
denied by these oarsmen, who reported that they were all alive and
well.

Surprisingly, cycling was the next sport to attract similar
attention. In the 1890s North Americans suddenly discovered the
bicycle, and medicine had another sport about which to express its
alarm. Prospective cyclists were warned that prolonged bending over
the handlebars could cause "kyphosis bicyclistarum" or in lay terms
"cyclist's stoop" or "cyclist's figure" or even "cyclist's spine".
Then, as expected, there was "cyclist's heart". The working life of
the heart was limited to only a certain number of heart beats, these
physicians asserted, and the faster heart rate during cycling would
only waste these precious beats and so lead to premature heart
failure.

One of the first references to the dangers of running on the heart
was made in 1909 by five eminent British physicians who started a
correspondence in the Times by stating that "school and
cross-country races exceeding one mile in distance were wholly
unsuitable for boys under the age of nineteen, as the continued
strain involved is apt to cause permanent injury to the heart and
other organs." Again, this view was easily refuted. From an analysis
of 16,000 schoolboys covering a period of twenty years, Lempriere
could find only two cases of sudden death during exercise that were
not due to accidents. He concluded that "heart strain through
exercise is practically unknown", a conclusion echoed by Sir Adolphe
Abraham, who denounced the concept of the strained athletic heart.

Running again became a medical cause célébre
in the 1970's as the popularity of the sport mushroomed. One of
the first articles to question the safety of such activity reported
that half of 59 sudden deaths occurred during or immediately after
severe or moderate physical activity, especially jogging. The authors
questioned "whether it is worth risking an instantaneous coronary
death by indulging in an activity, the possible benefit of
which.....has yet to be proved." They also considered "the possible
lethal peril of violent exercise to [heart-disease] patients."

On the other hand, in the early 1970âs a review of the
American Medical Joggers Association failed to document a single
death due to coronary atherosclerosis amongst athletes who had
completed marathons. The review suggested that athletes might be
protected from coronary artery disease. I formulated the "Bassler
hypothesis" which claimed that the absence of fatal coronary
atherosclerosis in marathon runners proved that marathon running
provided immunity against coronary artery disease and fatal
myocardial infarction. This optimism was reinforced by a boom in
marathon running in the mid-1970âs and increasing medical and
popular literature and media support for the sport.

One of the first reports disproving the Bassler hypothesis was
from a group in Cape Town who documented the presence of coronary
atherosclerosis in two marathon runners who died suddenly during
training. The authors concluded that marathon running could not
ensure absolute protection from coronary atherosclerosis. In a
subsequent publication, I and several other colleagues described 36
cases of sudden cardiac death in marathon runners, 75% of who had
coronary artery disease proven at angiography or autopsy.

More fuel was added to this controversy in the early 1980's by the
sudden death while running of James Fixx, the celebrated American
runner and author. Fixx had achieved international celebrity status
as author of the book that became an international best-seller
because it best captured the mood of the running explosion that
occurred in the late 1970s. Paradoxically, in a later book Fixx had
written an appropriate epitaph both to himself and to the concept
that runners could earn immunity from both heart disease and death:
"...runners are much like ordinary mortals. They can, sad to say, get
sick. They can even die."

Pathology of Sudden
Death

The first component of this issue that needs attention is whether
these deaths during exercise actually prove that exercise is the real
culprit and therefore a dangerous activity; or, stated differently,
whether exercise and sudden death are causally related. The
overriding conclusion from a large number of studies of sudden death,
including sudden deaths that occur during exercise, has shown that
virtually all persons who die suddenly during exercise have a serious
disease, usually of the heart, that adequately explains the cause of
death.

While a large number of cardiac conditions have been associated
with sudden death during exercise, the most common cause of death in
Westernized communities is coronary artery disease. Coronary artery
disease is the major cause of death in persons aged 40 or older.

Sportsmen below the age of 40 who die suddenly during exercise are
more likely to have hypertrophic cardiomyopathy. However, some young
athletes who die suddenly during exercise are likely to have severe
coronary artery disease as a result of familial hypercholesterolemia
(inherited high level of blood cholesterol).

Other less common causes of sudden death during exercise include
congenital anomalies of the coronary arteries, right ventricular
dysplasia, aortic rupture associated with Marfanâs syndrome,
coronary artery dissection, myocarditis and ill-defined conduction
disturbances presumed to be related to pathological changes found in
the conduction pathways at autopsy (Table 1).

Table 1: Causes of sudden death during
exercise in athletes

Conditions causing
myocardial ischemia

Atherosclerotic coronary artery disease

Coronary artery spasm

De novo coronary artery thrombus

Intramyocardial bridging

Hypoplastic coronary artery

Anomalous coronary arteries

Coronary artery dissection

Structural
abnormalities

Hypertrophic cardiomyopathy

Mitral valve prolapse

Valvular heart disease

Lipomatous infiltration of the right ventricle

Marfan's syndrome

Right ventricular dysplasia

Aortic stenosis

Sickle cell trait

Arrhythmias

Wolfe-Parkinson-White

Lown-Ganong-Levine

Long QT syndrome

Ventricular arrhythmias

Medial hyperplasia and intimal proliferation of the
main sinus node artery

Miscellaneous

Myocarditis

Anabolic steroid use

Cocaine abuse

Sarcoidosis

Non-penetrating chest trauma (commotio cordis)

But the more important point is that none of these conditions is
caused by exercise, however vigorous. Rather, the evidence is clear
that regular exercise acts against the development especially of
coronary atherosclerosis. There is also no evidence that exercise
accelerates the progression of these other potentially-lethal cardiac
conditions.

At present the exact mechanism causing exercise-related sudden
death in persons with established disease, especially of the coronary
arteries is not known. Whereas plaque rupture or thrombosis are
present in up to 95% of sudden cardiac deaths in the general
population, the incidence seems to be lower in exercise-related
deaths. Thus exercise-induced ischemia or coronary spasm may be
involved in exercise-related deaths.

In 1996 the Consumer Product Safety Commission described 38 deaths
(1973-1995) from baseball blows to the chest. Commotio cordis
predominantly affects children and adolescents 5 to 15 years of age
without pre-existing heart disease. Recently a swine model has been
developed which suggests that ventricular fibrillation may develop,
depending on the precise timing of the impact of a hard object,
traveling at speed, against the anterior chest wall. Impacts
occurring between 15 and 30 milliseconds before the T wave produced
ventricular fibrillation.

Effect
of Exercise on Risk of Sudden Death

Because athletes who die suddenly have advanced cardiac disease,
they are at high risk of dying suddenly, whether or not they
exercise. A number of studies have attempted to determine whether or
not exercise increases the risk that persons with advanced heart
disease will die suddenly during exercise rather than at rest. Some
have found that moderate exercise does not increase the risk of
sudden death, whereas other have found that more vigorous forms of
exercise such as cross-country skiing or running are associated with
a five- to seven-fold greater risk of sudden death.

Possibly the first detailed study of this question was reported by
Thompson and his colleagues. They found that, in the state of Rhode
Island between 1975 and 1980, 11 of 12 men died while jogging had
heart attacks. Five of these men were known to have heart disease
before their deaths. They calculated that the incidence of death
during jogging was one per 396,000 hours, which is about seven times
the estimated heart attack rate during more sedentary activities. In
this study the unequivocal evidence was that jogging increased the
risk that the jogger with severe heart disease would die while
exercising.

But this finding should not be used to overestimate the risk of
exercise. For example, in the Rhode Island study, there was one death
per 7,620 joggers per year--clearly an infinitesimal risk for each
individual jogger. Furthermore, it would be totally impractical to
screen all 7,620 joggers in Rhode Island in an attempt to identify
the one jogger at risk of sudden death each year. For example, on the
basis of these data, it has been calculated that a middle-aged jogger
with no known cardiac disease who decides to continue running for one
more year is at considerably lower risk of sudden death than is a
middle-aged non-runner who continues to ride in his car during that
year.

A recent study examining the prevalence of sudden cardiac death
during exercise was conducted on two groups of endurance runners
competing in the Marine Corps and Twin Cities marathons in the USA
held over a cumulative 30-year period. In the total of 215,413
runners who completed the races there were four exercise-related
sudden deaths due to unsuspected cardiac disease. Three of the sudden
cardiac deaths were due to coronary artery disease and one due to an
anomalous origin of the left coronary artery from the right sinus of
Valsalva. The overall prevalence of sudden cardiac death during the
marathon was thus 0.002%, strikingly lower than for several other
variables of risk for premature death calculated for the general US
population. The authors concluded that "although highly trained
athletes may harbor underlying and potentially lethal cardiovascular
disease, the risk of sudden cardiac death associated with physical
effort was exceedingly small (1 in 50,000) and as little as 1% of the
annual overall risk associated with living either with or without
heart disease."

Recently, Thompson reviewed several studies on the incidence of
sudden death during exercise. Thompson reported that the absolute
incidence of exercise-related sudden cardiac death to be 0.75 and
0.13 per 100,000 young male and female athletes and 6 per 100,000
middle-aged men die during exertion per year. Thus, while the
incidence of sudden cardiac death during exercise is very low, the
evidence suggests that exercise seems to trigger or cause sudden
cardiac death in athletes with underlying heart disease. Therefore,
the next important question is: if exercise does indeed increase the
risk of sudden death, by how much did exercise actually shorten the
life expectancy of the patient who was in any case at high risk of
dying suddenly and unexpectedly? Indirect evidence that the exercise
probably does not greatly decrease life expectancy under such
circumstances comes from a study of the 1978 Rhode Island blizzard.

In February 1978 a severe blizzard struck Rhode Island causing the
daily death rate from heart attack to increase from the usual
February average of 27 to 48 deaths per day. This rate remained high
for three of the first five days after the storm, but subsequently
decreased below the normal daily average, so that the total heart
attack deaths for February that year was the same as for previous
years. Thompson concluded that: "These results suggest that the added
physical and emotional stress arising from the storm eliminated those
who would have succumbed to ischemic heart disease (heart attack) in
the near future." In the same way, jogging deaths may occur in those
whose time is up and who were due to die within the next few day or
weeks even if they avoided all forms of exercise, including walking.

The data of Siscovick and his colleagues clearly show that persons
who have undetected heart disease and who are therefore at risk of
sudden death, reduce their overall risk of sudden death if they
exercise regularly. During exercise, however, their risk is increased
acutely. The researchers collected detailed information on all
persons dying suddenly during a one-year period in Seattle,
Washington. They then excluded from their analysis all those persons
who were ill, who had been off work or who had experienced any
symptoms before their sudden deaths. They were left with a total of
145 sudden deaths in a group of persons who were for all intents and
purposes healthy right up to the moment that they suddenly died.
Analysis of these data showed that those persons who exercised
vigorously on a regular basis had an overall risk of sudden death
about two-thirds that of the non-exercisers.

Interestingly, though, the risk of sudden deaths in the exercising
group while these persons were exercising was increased acutely for
the duration of the exercise bout, above the overall risk of the
non-exercisers. Thus although the total group of exercisers had a
reduced risk of sudden death, that subset of exercisers with advanced
heart disease resistant to all preventive measures including
exercise, and who would ultimately die suddenly, were more likely to
die while they were exercising rather than when they were at rest.
This finding explains why the sudden death of athletes usually occurs
during exercise and why such events must not be construed to indicate
that exercise is dangerous and to be avoided. In fact, if the
exercisers were to stop exercising, their risk of sudden death would,
according to these data, increase about threefold.

To put these findings in perspective, consider the following.
Studies show that in the population of about 10,000 Comrades Marathon
runners there are approximately 3 sudden deaths per year, most of
which occur as predicted by the data of Siscovick and his colleagues,
during or shortly after exercise. If, on the basis of these three
deaths per year, it was decided that marathon running was too
dangerous and was summarily and effectively banned, the annual risk
of sudden death in the group of ultra-marathon runners would
approximately triple. Thus each year after the banning of marathon
running, there would be nine, not three, sudden deaths; clearly an
undesirable result. But by encouraging the cohort of 10,000 marathon
runners to continue running, about six lives per year are being
saved.

In summary, the studies of Siscovick and his colleagues confirm
the finding that the risk of sudden death is reduced in persons who
exercise regularly and suggest that this is almost certainly not due
to the presence of confounding variables. However, these studies also
show that there is an increased likelihood that those persons who
have heart disease in spite of their regular exercise, will die
during the short period that they spend exercising. Were such persons
to avoid all exercise however, their overall risk of sudden death
would be increased, not decreased. The higher the level of coronary
risk, the greater the degree of benefit from exercise. Persons who
are at low risk of dying suddenly from coronary heart disease benefit
less from vigorous physical exercise than do those who are at high
risk, either because of a family history of heart disease, or because
they are smokers who have other risk factors already described. As
Siscovick and colleagues stated, "efforts to discourage clinically
healthy persons at risk of primary cardiac arrest from continuing to
engage in vigorous exercise may be inappropriate."

Levels
of Physical Fitness

It is important to stress that severe heart disease may be present
even in person who are extremely physically fit. For example, we have
reported cases of marathon runners who completed the 90-km Comrades
Marathon only weeks before their subsequent deaths from severe
advanced coronary artery disease, in some cases with associated
hypertrophic cardiomyopathy. One 42 year-old runner completed a 42.2
km standard marathon in 3 h 6 min just three weeks before autopsy
showed he had complete occlusion of one major coronary artery and 75%
narrowing, with atherosclerosis, of the other two. In addition, there
was evidence of hypertrophic cardiomyopathy. The case of the American
runner who died within a minute of setting a regional running record
in the United States has already been described. More recently,
Sergei Grinikov, a 28 year-old double Olympic gold medalist,
collapsed and died suddenly whilst training. His autopsy revealed
coronary artery disease.

Warning Symptoms

Persons who die suddenly during exercise frequently have warning
symptoms of heart disease which they ignored, choosing to continue
exercising rather than to seek medical advice. Thus, my 1987 study of
heart attacks and sudden deaths in marathon runners found that fully
81% of these cases had warning symptoms. Six athletes completed
marathon races, and three the Comrades Marathon, despite symptoms of
chest or abdominal pain sufficiently severe to force them to stop
running and to walk and run intermittently. Despite severe chest
pain, one athlete continued to run a 16-km race and collapsed at the
finish. Another runner continued training for three weeks, including
a 64-km training run with chest pain severe enough to force him to
walk on numerous occasions.

Lessons from James Fixx's
Death

Many of these points were rather tragically illustrated by James
Fixx's death while running. Fixx was at high risk of heart disease
because his father had died from a heart attack at a relatively very
young age (43 years). In addition, Fixx was a reformed smoker with a
markedly elevated blood cholesterol concentration. Fixx had also
experienced warning symptoms which he chose to ignore and had refused
the option of undergoing a maximal exercise stress test.

Autopsy showed that Fixx had severe coronary artery disease with
near total occlusion by atherosclerosis of one and 80% occlusion of
another coronary artery. There was also evidence of a recent heart
attack. In addition, the heart was somewhat large suggesting the
possibility of concurrent hypertrophic cardiomyopathy.

On the day James Fixx died, 1000 other Americans would also have
died of heart attacks. Few if any would have received nationwide
coverage. Yet almost all of those deaths would have occurred in
persons who were sedentary, or were smokers, or who had uncontrolled
high blood pressure and elevated blood cholesterol concentrations. If
only those sudden deaths occurring in athletes are reported in the
press, it is understandable why the public acquire a distorted
impression of the relationship between exercise and heart disease.

Thus James Fixx's death followed a familiar pattern and helps
emphasize the points already made. One interesting possibility not
considered by many is that regular exercise actually allowed James
Fixx to outlive his father by nine years. This possibility would be
supported by the scientific findings, especially of Siscovick and his
colleagues.

Factors Triggering
Events

There are three postulated mechanisms by which vigorous physical
activity may precipitate myocardial ischemia in athletes with
coronary artery disease. First, the initial surge of blood pressure
with initiation of exercise might precipitate the fissuring of a
vulnerable atherosclerotic plaque with the subsequent thrombus
formation transforming a previously non-occlusive lesion into a total
occlusion. Second, it is possible that a non-occlusive
atherosclerotic plaque may precipitate transient ischemia by inducing
an imbalance between myocardial oxygen demand and supply. As fewer
than one-third of resuscitated athletes subsequently develop evidence
of acute myocardial infarction, it is thought that this is the most
common mechanism of sudden cardiac death during exercise. Third,
myocardial ischemia during exercise might result from coronary-artery
spasms, which occur most commonly at sites of established
atherosclerosis.

Irrespective of which of the above mechanisms is responsible for
the occurrence, the event immediately preceding all cases of sudden
cardiac death during exercise is a massive reduction of cardiac
output (secondary to either myocardial ischemia or arrhythmia),
decreased cerebral blood flow, and loss of consciousness. It is
believed that a combination of the triggering event and a susceptible
myocardium combine to initiate potentially lethal arrhythmias
especially ventricular fibrillation. The fall in cardiac output upon
rapid cessation of exercise and the presence of arterial
vasodilatation are additional factors that might explain the
relatively frequent occurrence of sudden cardiac death in the
immediate post-exercise period. Postulated pathophysiological factors
during physical exertion that may lead to triggering events or a
susceptible myocardium are listed in Table 2.

Table 2: Pathophysiological factors during
physical exertion that may lead to triggering events or a
susceptible myocardium

Elevated myocardial oxygen demand and simultaneous
shortening of diastole and coronary perfusion time

Alterations of parasympathetic and sympathetic tone

Release of thromboxane A2 and other coronary
vasoconstrictors

Enhanced blood coagulation

Increased blood lactate concentrations (lactic
acidosis)

Intra- and extracellular electrolyte derangements

Increased serum free fatty acid concentrations

Excessive rise in body temperature

Exercise as a Protective
Mechanism

Exercise has been shown to reduce the rate of development of
coronary atherosclerosis in monkeys fed a high-fat atherogenic diet
and to increase the resistance of the trained heart to ventricular
fibrillation, the lethal abnormal heart rhythm that causes most
persons with heart disease to die suddenly. Another potentially
important mechanism for this effect is simply the reduction of the
coronary risk factors. For example, in one survey 81% of men and 75%
of women who were smokers stopped smoking when they started running.
Similarly, subjects taking up marathon running show beneficial
changes in coronary risk factors.

Screening for Risk
Factors

When approached by a patient who wishes either to commence
exercise or to establish that it is safe for him or her to continue
exercising at their present level, the clinician's first
responsibility is to rule out the presence of the acute or chronic
diseases associated with sudden death. The clinical problem has
several challenges. First, the incidence of such diseases in the
exercising population is extremely low with estimated incidences
varying from 1 per 10,000 active exercisers to 1 per 200,000 in
children and young adults. Secondly, it is extremely difficult to
detect some of these latent forms of heart disease. Indeed, some
athletes might have a 30-60% non-critical lesion that does not
produce ST segment changes or angina during exercise testing. Third
is the finding that most acute coronary events occur due to rapid
progression of disease at sites at which a critical lesion was not
previously present. Furthermore, even when latent disease is
detected, it is not always possible to differentiate absolutely those
with the disease who will die suddenly during exercise from those
with the same condition who are not at risk.

It is clear that there are many people with latent heart disease,
especially coronary heart disease, who are able to exercise quite
safely without the risk of sudden death. How these are to be
distinguished on clinical grounds from those at risk of sudden death
during exercise has yet to be established. Accordingly a more
pragmatic approach would seem justified. The following guidelines
probably represent the current consensus.

All persons over 50 should undergo cardiovascular screening before
starting any type of exercise program. Younger persons (less than 50
years of age) who are either already participating or who wish to
start exercising should first be interviewed for a family history of
conditions associated with sudden death and screened for symptoms and
clinical signs of cardiovascular disease, and for risk factors for
heart disease. When either the family history is suggestive, or
clinical suspicion is raised, or risk factors such as hypertension,
hypercholesterolemia or cigarette smoking are present, subjects
should undergo maximal exercise testing for measurement of exercise
performance and the electrocardiographic response to exercise. When
abnormalities are detected, further specialist cardiological
investigation including echocardiography and possibly coronary
angiography is indicated. Conditions in which echocardiography is
useful in the evaluation of athletes are listed in Table 3. Subjects
with identified cardiac disease should then exercise under
supervision, at least initially.

Table 3: Conditions in which echocardiography
is used in evaluating athletes

Suspected congenital heart disease

Hypertrophic cardiomyopathy

Right ventricular dysplasia

Pericarditis

Myocarditis

Ischemic heart disease

Suspected valvular disease

Unexplained cardiac murmur

Unexplained abnormal ECG

Anomalies of the coronary arteries

Arrhythmias

But even when these guidelines are followed, less than 20% of
subjects at risk of developing a cardiac event during exercise will
be identified. Thus Siscovick and his colleagues have argued that
routine exercise testing is of limited value for assessing the risk
of exercise in middle-aged men. Similarly, Thompson and colleagues
have suggested the "physicians can recommend exercise to asymptomatic
adults without great concern for possible cardiovascular
complications... The risk of exercise is small and suggests that the
routine exercise testing of healthy subjects before exercise training
is not justified."

The recommendations that I have made specifically for persons who
are already active in sport are based on studies of sudden death in
marathon runners. These include:

Runners should not assume that completing a marathon will
ensure total immunity from coronary heart disease or that
reattainment of that distance after a heart attack will prevent
progression of that disease;

Runners should seek medical advice and not force themselves
when exertional symptoms develop;

When consulted by symptomatic runners, doctors should not
exclude the possibility of coronary or other life-threatening
heart diseases such as hypertrophic cardiomyopathy, simply because
the athlete is physically fit.

There is a much lower prevalence of coronary artery disease in
females younger than 65 years. Indeed females of 45 years of age,
with a typical history of angina pectoris, have only a 55%
likelihood of coronary atherosclerosis, whereas the same clinical
findings in a 65 year-old female imply a greater than 90% chance
of having significant coronary artery disease. Furthermore,
diagnostic exercise testing is less accurate in women, because
there is a higher rate of false-positive and false-negative tests.
Therefore exercise testing using either thallium scintigraphy or
echocardiography greatly improves the diagnostic accuracy of
exercise tests in females.

In brief, this experience is in agreement with the conclusion of
Thompson and colleagues to the effect that only athletes who
are symptomatic should be exhaustively tested and discouraged from
exercise when a life-threatening cardiac abnormality is discovered.
Because in my experience the majority at least of adults who die
suddenly during exercise, like James Fixx, have warning symptoms,
this simple procedure could possibly reduce the incidence of sudden
death during exercise by as much as 80%. Unfortunately, the condition
will never be completely prevented because in about 20% of persons,
sudden death remains the first symptom of heart disease that they
experience. Some may even have undergone maximal exercise testing
without incidence within a reasonably short time before their
subsequent deaths.

While most emphasis is placed on the detection of latent coronary
heart disease, detection of other conditions is also important. Thus
persons with hypertrophic cardiomyopathy are at increased risk of
sudden death during exercise. Current practice is that persons with
this condition are encouraged to avoid all forms of physical
activity, however gentle. Whether this is appropriate, and whether
all forms of hypertrophic cardiomyopathy carry an equivalent risk of
sudden death is not yet known. Even so, current practice is probably
that the physical activity of persons with this condition should be
restricted.

With regard to rheumatic heart disease, it seems that severe
aortic stenosis is the form of valvular disease most frequently
associated with sudden death. Furthermore, deaths in persons with
rheumatic heart disease almost always occur in those in whom the
diagnosis of serious heart disease is well established and whose
exercise tolerance had already been severely restricted by their
disease. Thus only those patients with rheumatic heart disease whose
exercise tolerance is already restricted should further reduce
physical activity. There is no firm evidence that the physical
activity of asymptomatic persons with clinical evidence of (mild)
valvular dysfunction as a result of rheumatic heart disease needs to
be restricted, nor that physical activity detrimentally influences
the course of their disease. It must be remembered that the heart of
a person with rheumatic heart disease must beat 24 hours a day
despite unfavorable hemodynamic loading. It is unlikely that the
additional hemodynamic stresses of even one hour of exercise a day
would materially influence the adaptations already made to compensate
for the hemodynamic abnormalities caused by the valvular disease.

With regard to myocarditis, there is the question that it is a
cause of sudden death in persons recovering from a viral infection.
Accordingly, persons who suffer from a viral infection or who have
had systemic manifestations of the infection (fever, myalgia and
arthralgia) should be encouraged not to exercise vigorously for at
least 14 days after their body temperature returns to normal and
their myalgia and arthralgia subside. A persistent increase in the
resting heart rate would also indicate continuing myocardial
involvement and would be an absolute contraindication to vigorous
exercise.

The screening of young athletes for potentially fatal
cardiovascular disease has received special attenion by the American
Heart Association, who have set the following recommendations. These
can be applied also to the older exercising population:

Mandatory pre-participation medical screening including
medical and family history and physical examination for all
athletes.

Pre-participation evaluation to be conducted before high
school and repeated every 2 years.

Athletic screening to be performed by an appropriately trained
medical professional.

Auscultation of the heart to be conducted while the patient is
lying and then standing, to identify structural cardiovascular
abnormalities.

With respect to the long QT syndrome, recently three genes have
been identified that indicate which persons with the long QT syndrome
are likely to suffer fainting episodes and to die during physical
exertion. A blood-screening test is in development and should be
available by mid 1999.

Finally, detection of many of the other conditions listed in Table
1 may be difficult. When identified, the clinician must still decide
whether the risk of sudden death posed by the condition exceeds the
benefits the patient might expect from continuing to participate in
regular exercise.

Summary

Sudden death in athletes will always be an emotive topic, for
it suggests that athleticism may not prevent the development of
heart disease and may actually increase the likelihood that the
athlete will die suddenly during exercise.

Persons who die suddenly during exercise have advanced heart
disease of which they are frequently unaware. The commonest forms
of heart disease associated with sudden death during exercise are
coronary artery disease and hypertrophic cardiomyopathy. Less
common cardiac conditions linked to sudden death in athletes
include anomalous origin of the coronary arteries, aortic rupture
associated with Marfan's syndrome, myocarditis, mitral valve
prolapse and various arrhythmias.

The incidence of these predisposing diseases in the athletic
population is extremely low, possibly of the order of 1 per 10,000
to 1 per 200,000 athletes. Detection of some of these conditions
in asymptomatic athletes may be difficult, if not impossible.

Regular exercise reduces the overall risk of sudden death in
persons with latent coronary artery disease, yet acutely increases
the risk of sudden death during exercise for those with heart
disease that predisposes to sudden death.

In practical terms, only athletes with symptoms or clinical
signs of, or risk factors for coronary or other forms of heart
disease should undergo routine maximal exercise testing when they
commence an exercise training program. However, once symptoms
suggestive of cardiac disease are present in athletes, detailed
cardiological testing is mandatory.

Further Reading

American Heart Association. (1992).
Statement on exercise: benefits and recommendations for physical
activity programs for all Americans; a statement for health
professionals by the committee on exercise and cardiac rehabilitation
of the Council on Clinical Cardiology, American Heart Association
(position statement). Circulation, 86, 340-344.

Braden, D.S., & Strong, W.B.
(1988). Preparticipation screening for sudden cardiac death in high
school and college athletes. Physician and Sportsmedicine, 16(10),
128-140.